> In data types! Yes. With guardrails. I mean, I do a lot of writing in JS/TS but I'd never write something that tacked a dynamic property onto some class and

> In data types! Yes. With guardrails. I mean, I do a lot of writing in JS/TS but I'd never write something that tacked a dynamic property onto some class and picked it up later. That's just gauche. > a black box that takes type x as input and produces type y as output I agree, but I'd rather keep that function in Class X. If it's specific and X is a final/protected class, I'd say `protected doSomething()=>Y` where the argument is the implicit `this`. I'd never allow some other thing to run this function, definitely not some other object floating out there; if it were going to be run that way it would have to be a `static DoSomething(x:X)=>Y` ...but I would still keep it in the file for X.